1. Field of the Invention
The present invention relates to disconnect devices—releasable connectors—that are used downhole in oil or gas wells. The invention is particularly, though not necessarily exclusively, relevant to hydraulic disconnects as are used in coiled tubing workstrings to release the bottom hole assembly of the workstring in a controlled fashion.
2. Description of the Related Art
Hydraulic disconnect devices have been in use for many years and usually work along the following basis. Referring to FIG. 1 of the accompanying drawings, here the disconnect device takes the form of a tubular body 2 that is an intermediate sub between an upper sub 1 and lower sub 3 of the workstring. This tubular body, or intermediate sub, 2 accommodates a tubular mandrel/bobbin 4 extending along its bore and which is retained in an initial position as illustrated by shear screws/pins 5. This mandrel/bobbin 4 in its initial position cooperatively engages with and thereby supports a collet 6 that is integrally assembled with the lower sub 3 and thereby the upper sub 1 supports the lower sub 3 by the mandrel 4 and collet 6. The collet 6 takes tensile loads on the workstring, preventing the disconnect from being parted during normal use of the workstring until the disconnect is actuated by hydraulic control.
In order for the disconnect to have torsional capabilities as well as transferring tensile loads, special keying castellations need to be provided on the tool.
To actuate the disconnect to release the joint, a steel ball 7 is dropped down the bore of the workstring to fall the level of the disconnect device and seat on the top of the bobbin/mandrel 4, blocking the bore of the mandrel 4 and forming a pressure tight seal against it so that when fluid pressure is applied over the mandrel 4 this acts over the diameter of the seal and the applied force shears the shear pins/screws 5, allowing the mandrel 4 to move downwards to its second position. When the mandrel 4 is in its second position, undercuts that are provided within the mandrel 4 are aligned with protrusions on the fingers of the collet 6 whereby the mandrel 4 no longer supports the collet 6 and the joint is able to be parted. The lower sub 3 and associated components are left down hole as the workstring is retracted. They can subsequently be retrieved using standard fishing tools that are able to latch in the profile previously occupied by the collet 6. However, the castellations provided on the body associated with the lower sub 3 can be obstructive and interfere with the attempts to fish out the bottom hole assembly.
In another prior art system (not illustrated) the disconnect device has, instead of a collet, a set of turned slips that are supported on a mandrel accommodated in the bore of the disconnect body. These slips are generally formed by splitting a tubular component into segments, the component having been turned through 360° to provide a circumferential recess. These slips are more compact, needing less workstring length, than the corresponding collet-based prior art system. They are arranged to locate into a secondary internal profile and hence when parted give a clean fresh fishneck profile for future retrieval operations. As with the collet system, however, because they have a turned, 360° circumferential, profile they lack any torsional capacity and are accordingly provided with keying castellations. As with the collet-based device, these castellations can interfere with fishing operations.